Wireless Collection of Fastener Data

ABSTRACT

Data is remotely collected from a plurality of fasteners in response to a query signal wirelessly transmitted by a reader. Each of the fasteners includes a sensor for measuring a parameter related to the stress on the fastener. A device adapted to be attached to each of the fasteners receives the query signal, activates the sensor to measure the parameter and wirelessly transmits the data including the parameter to the reader.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims benefit to U.S. patentapplication Ser. No. 14/328,325 filed Jul. 10, 2014 and entitled“Wireless Collection of Fastener Data,” which is a continuation of U.S.patent application Ser. No. 12/691,796 filed Jan. 22, 2010 entitled“Wireless Collection of Fastener Data,” now issued as U.S. Pat. No.8,810,370. This application is also related to U.S. patent applicationSer. No. 12/582,885 filed Oct. 21, 2009 now issued as U.S. Pat. No.8,521,448; Ser. No. 12/582,855 filed Oct. 21, 2009; Ser. No. 11/931,628filed Oct. 31, 2007 now issued as U.S. Pat. No. 7,703,669; Ser. No.12/552,895 filed Sep. 2, 2009 now issued as U.S. Pat. No. 8,978,967; andSer. No. 12/536,438 filed Aug. 5, 2009 now issued as U.S. Pat. No.8,683,869, all of which applications are incorporated by referenceherein in their entireties.

TECHNICAL FIELD

This disclosure generally relates to structural fasteners, and dealsmore particularly with the remote wireless collection of data from thefasteners, such as the stress on a fastener.

BACKGROUND

It is sometimes necessary to periodically check the status of fastenersused to clamp structural joints. For example, in the case of vehiclessuch as aircraft, the clamping force applied by fasteners in certainmission critical structural joints and assemblies must be maintainedwithin prescribed limits. Periodic monitoring of fastener clamping forcemay be necessary because of the tendency of some structures to relaxover time, and physical changes in the fasteners such as work hardeningand creep, all of which may result in a change in the preload applied bya fastener, and thus the stress on the fastener. Where fastener preloadis found to be outside of the prescribed limits, it may be necessary tore-torque the fastener, or replace it. In the past, monitoring suchfasteners was performed by maintenance technicians who would physicallycheck and record the status of the fasteners, including the level offastener preload. This manual process was time-consuming and laborintensive, and could sometimes be difficult to perform where thefasteners were located in areas not easily accessed.

More recently, fasteners have been devised that incorporate a sensorwhich measures the stress, and thus the preload, on the fastener.However, in order to read the measured preload and associate it with theparticular fastener being read, a technician must physically contact thefastener with a reader that reads the preload as well as a bar code thatuniquely identifies the fastener. This approach to collecting fastenerdata can also be time-consuming, labor intensive, and difficult toperform where fastener access is limited. In some cases, where fastenersare located within a sealed-off area or a particularly smallcompartment, such as the tail section of an aircraft, it may not bepossible to make physical contact with the fastener, thus precludingmeasurement of fastener preloads.

Accordingly, there is a need for a non-contact method and apparatus forremote collection of data from fasteners, such as the preload or stresson a fastener. There is also a need for a method and apparatus that maybe adapted for monitoring existing types of fasteners, even where it maybe difficult or impossible to physically access the fasteners.

SUMMARY

In accordance with the disclosed embodiments, a non-contact method andapparatus is provided for remotely monitoring the status of fasteners,including measuring and wirelessly collecting one or more parametersindicative of fastener status. The method uses wireless communicationsbased on any of several wireless techniques, and can be used to collectdata where the fasteners are located in areas of a structure that aredifficult to physically access. The method allows a fastener ID to bereliably associated with a corresponding stress value. The apparatususes wireless communication devices that may be easily retrofitted toexisting types of fasteners. The remote, wireless collection of fastenerdata provided by the disclosed embodiments may substantially reducelabor costs by reducing or eliminating the need for manual inspectionsby technicians that require touch labor, while allowing more frequentchecks of fastener status.

According to one disclosed embodiment, apparatus is provided forcollecting data from a plurality of fasteners, each including a sensorfor measuring the stress on the fastener. The apparatus includes adevice adapted to be attached to each of the fasteners for wirelesslytransmitting data related to the measured stress, and a reader forwirelessly reading the data transmitted by the device. The device mayinclude a cap attachable to the fastener as well as an antenna and awireless transmitter in the cap that is used to transmit the data to thereader. The reader may include a transmitter for wirelessly transmittinga signal to each of the devices. Each of the devices may further includea wireless receiver in the cap for receiving the signal from the readerand means for converting the signal into energy and for storing theenergy. The device may include means in the cap for converting thestored energy into a pulse used to activate the sensor. The receiver maycomprise one of an infrared signal receiver, a radio frequency signalreceiver and an acoustic signal receiver.

According to another embodiment, apparatus is provided for collectingdata from a plurality of fasteners, each including a sensor formeasuring the stress on the fastener. The apparatus includes a readerfor wirelessly transmitting a first signal along a relatively narrowpath to the fastener and means on the fastener for receiving the firstsignal. The apparatus further includes means on the fastener forwirelessly transmitting a second signal to the reader containing datarelated to the stress measured by the sensor. The reader may include atransmitting antenna for forming the first signal into a relativelynarrow beam. The receiving means on the fastener may include adirectional antenna for receiving the first signal along the narrowpath.

According to another disclosed embodiment, a method is provided ofcollecting data from a plurality of fasteners. The method includeswirelessly transmitting a first signal from a reader along therelatively narrow path to the fastener, and receiving the first signalat the fastener. The method also includes sensing at least one parameterat the fastener, and wirelessly transmitting a second signal related tothe parameter from the fastener to the reader. The wireless transmissionof the first signal from the reader may be performed using a directionalantenna or a beam of energy. The energy beam may comprise radiofrequency electrical energy, light energy and acoustic energy.

According to a further embodiment, apparatus is provided for collectingdata from a plurality of fasteners each including a sensor for measuringthe stress on the fastener. The apparatus includes a device adapted tothe attached each of the fasteners for sensing the temperature of thefastener and for wirelessly transmitting data related to the measuredstress and the sensed temperature. The apparatus may also include areader for reading the data transmitted by the device. The device mayinclude a cap attachable to the fastener, a temperature sensor in thecap, and a wireless transmitter in the cap for transmitting the data tothe reader.

According to a further embodiment, a method is provided of collectingdata related to the stress on a fastener. The method includes the stepsof sensing at least one temperature varying parameter on the fastenerrelated to the stress on the fastener, sensing the temperature of thefastener and adjusting the parameter based on the sensed temperature.Sensing the temperature is performed using a sensor at the fastener.

According to another embodiment, apparatus is provided for collectingdata from a plurality of fasteners installed on a structure, whereineach of the fasteners includes a sensor for measuring the stress on thefastener. The apparatus includes a device on each of the fastenerscoupled with a sensor for wirelessly transmitting an acoustic signalthrough the structure representing the measured stress. The apparatusalso includes a reader for reading the acoustic signal. The device mayinclude a cap attachable to the fastener, and a transducer in the capfor transmitting the acoustic signal through the structure. The devicemay include an acoustic coupler adapted to the structure for couplingthe acoustic signal from the transducer to the structure. The reader mayinclude an acoustic transducer for converting the acoustic signal intoelectrical energy, and an acoustic coupler for acoustically coupling thetransducer with the structure.

According to another embodiment, a method is provided of collecting datafrom a fastener on a structure. The method includes sensing at least oneparameter at the fastener, and transmitting an acoustic signal includingthe sensed parameter from the fastener through the structure. The methodfurther includes reading the acoustic signal. Transmitting the signalmay be performed by directing the signal along a relatively narrow paththrough the structure. The method may also include selecting a frequencyfor the acoustic signal based ay least in part on characteristics of thestructure.

The disclosed embodiments provide a method and related apparatus forremotely and wirelessly collecting data from fasteners installed on astructure which allow monitoring of fasteners in areas of the structurethat are difficult to access and which may reduce hand touch labor.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is an illustration of a functional block diagram of apparatus forwirelessly collecting data from a fastener installed on a structure.

FIG. 2 is an illustration of a fastener and a timing plot useful inexplaining timing measurements related to preload on the fastener.

FIG. 3 is an illustration of a top view of a fastener having a capinstalled thereon.

FIG. 4 is an illustration of a sectional view taken along the line 4-4in FIG. 3.

FIG. 5 is an illustration of a functional block diagram of an electroniccircuit contained within the fastener cap shown in FIGS. 3 and 4.

FIG. 6 is an illustration of a flow chart of a method of wirelesslycollecting fastener data using the cap device shown in FIGS. 3-5.

FIG. 7 is an illustration of a flowchart of an alternate method ofcollecting fastener data.

FIG. 8 is an illustration of a combined block and diagrammatic viewshowing collection of data from fasteners installed on an aircraft.

FIG. 9 is an illustration of a method and apparatus for collecting datafrom fasteners using directional signals transmitted along relativelynarrow paths.

FIG. 10 is an illustration of the use of a laser beam to aid in aiming adirectional antenna on a reader.

FIG. 11 is an illustration similar to FIG. 10 but showing thetransmission of a radio frequency query signal to the fastener after thereader has been aimed.

FIG. 12 is an illustration showing the use of a dish type antenna fortransmitting radio frequency signals along a relatively narrow path to afastener.

FIG. 13 is an illustration of the use of a lens to focus infrared energyinto a beam used to query a fastener.

FIG. 14 is an illustration showing the use of a dish reflector toconcentrate infrared energy produced by a diode.

FIG. 15 is an illustration showing the use of a laser to aim an infraredtransmitter forming part of a reader.

FIG. 16 is an illustration similar to FIG. 15, but showing the use of avisible light source to aim the infrared transmitter on the reader.

FIG. 17 is an illustration of a side view of a reader that includes apistol grip and optical sight for aiming the reader toward a fastener.

FIG. 18 is an illustration of a reader that includes a temperaturesensor for remotely sensing the temperature of a fastener or thestructure surrounding the fastener.

FIG. 19 is an illustration of a perspective view of a reader having anon-contact temperature sensor and a pistol grip to aid in aiming thereader.

FIG. 20 is an illustration of a flow chart showing a method ofcollecting fastener data which includes adjustments based on the sensedtemperature of the fastener.

FIG. 21 is an illustration of a functional block diagram of thecomponents of a reader including a remote temperature sensor.

FIG. 22 is an illustration of a combined block and diagrammatic view ofa reader employing an acoustic signal to query fasteners.

FIG. 23 is an illustration similar to FIG. 22 but showing an acousticreader using a focused acoustic signal to query the fasteners.

FIG. 24 is an illustration of a functional block diagram of an acousticreader and a fastener equipped with an acoustic transducer.

FIG. 25 is an illustration of a method of collecting fastener data usingacoustic energy communications.

FIG. 26 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 27 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIG. 1, the disclosed embodiments relate to a device36 that may be attached to a fastener 30 in order to adapt the fastener30 for wireless communications with a remote reader 38. The fastener 30may be installed on a structure 34 and may comprise any of a wide rangeof hardware devices used to mechanically join, affix or clamp two ormore members together. For example, the fastener 30 may comprise,without limitations, a bolt, a screw, a stud, a clamp or a pin, to nameonly a few. The fastener 30 includes a sensor 32 which measures one ormore parameters that are related to the status or a condition of thefastener 30. For example, the sensor 32 may comprise a transducer thatmeasures a parameter related to the stress, and thus the preload on thefastener 30.

In one embodiment, the device 36 may be programmed to periodicallytransmit the measured parameter to the reader 38 so that the status ofthe fastener 30 may be monitored. In another embodiment, the reader 38may query the fasteners 30 by periodically transmitting wireless signals(hereinafter sometimes referred to as “query signals”) to the device 36which results in activation of the sensor 32 to measure the desiredparameter. The measured parameter is wirelessly transmitted by thedevice 36 to the reader 38 where the parameter may be read or may beused in calculations to determine the status of the fastener 30, such asthe stress on the fastener 30. In other embodiments, calculations todetermine the stress value may be performed by the device 36 which thenwirelessly transmits the stress value to the reader 38. The reader 38may provide a visual and/or audible signal to the user indicating that aparticular read cycle has or has not been successfully carried out.

Attention is now directed to FIGS. 2, 3 and 4 which illustrateadditional details of the fastener 30 and the device 36. As best seen inFIG. 4, the fastener 30 is depicted as a bolt having a head 56, and ashank 44 that passes through a structure 34 comprising a pair of plates34 a, 34 b. The lower end 45 of the shank 44 is provided with externalthreads (not shown) which receive a threaded nut 62. The head 56includes a shoulder 60 which clamps a washer 74 against plate 34 a whenthe head 56 and/or the nut 62 are tightened in order to apply a clampingforce which holds the plates 34 a, 34 b together.

The preload, and thus the stress on the fastener 30 is a function, inpart, of the clamping force applied by the fastener 30 to the structure34. The device 36 includes a cap 66 formed of a suitable rigid materialsuch as a metal, however in some applications it may be possible to formthe cap 66 from composites or other high strength materials. The cap 66includes a head 68 which, in the illustrated example, is generallycircular, however other shapes are possible. For example, the head 68may include wrench flats (not shown) forming a hexagonal or octagonalshape suitable to be engaged by a wrench (not shown) employed forinstalling the device 36 on the fastener 30.

The cap 66 further includes inclined sides 70 which surround the head 56of the fastener 30 and include a ring shaped bottom 78 that may engagethe structure 34. The cap 66 includes a circumferential recess 72therein, near the base 78, which complementally receives an upturnedflange 76 on the outer periphery of the washer 74. Thus, the cap 66 isattached to the fastener 30 by the flange 76 which retains the cap 66 onthe head 56 of the fastener 30.

The device 36 also includes an electronic circuit 86 housed within thecap 66. In one embodiment, an antenna 88 connected with the circuit 86may be integrated into the head 68 of the cap 66, while in anotherembodiment, the antenna 88 a may be integrated into the sides 70 of thecap 66. In yet another embodiment, the both antenna 88 and 88 a may beintegrated into the cap 66.

The head 56 of the fastener 30 includes a central recess 64 containing asensor 32 which will be discussed in more detail below. The sensor 32measures at least one parameter indicative of the status of the fastener30 which is either transmitted directly to the reader 38 (FIG. 1), orused in calculations performed by the circuit 86 to determine the statusof the fastener 30. The cap 66 is sealed to the head 56 of the fastener30 around the periphery of the recess 64 by means of a compressibleO-ring 80, thereby sealing the recess 64 against intrusion of moistureand/or foreign particles. The device 36 further includes a pair ofelectrical contacts 82, 84 which are coupled with the circuit 86 andrespectively contact the sensor 32 and fastener head 56 when the cap 66is installed on the fastener 30. An optional temperature sensor 90mounted on the cap 66 is coupled with the electrical circuit 86 andcontacts the fastener head 56 in order to measure the temperature of thefastener 30, or the temperature of the structure 34 immediatelysurrounding the fastener 30.

As previously indicated, the washer 74 adapts the cap 66 to be attachedto the head 56 of the fastener 30. However, it may be possible to attachthe device 36 to other parts of the fastener 30, or to the nut 62 usingother attachment techniques that may not require the use of the washer76. In one embodiment, the cap 66 and the washer 76 may be configured toprovide a bayonet type mounting (not shown) so that the cap 66 isattached to the fastener 30 by a twist-on action. Alternatively, it maybe possible to provide threads (not shown) between the cap 66 and thefastener 30 and/or washer 74 which adapt the cap 66 to be screwed ontothe fastener 30 and/or the washer 74. From the foregoing then, it may beappreciated that existing fasteners 30 may be retrofitted with thedevice 36 by installing the washer 74 and then attaching the cap 66 tothe washer 74 using a twist-on motion. In some embodiments, the cap 66may be removed from the fastener 30 with a reverse, twist-off motion inorder to allow repair or replacement of the cap 66.

Referring now particularly to FIG. 2, the sensor 32 may comprise any ofa variety of sensors or transducers using any of various technologiessuitable for measuring one or more parameters indicative of the statusof the fastener 30, including but not limited to those that may be usedto determine the stress or preload 40 in the fastener 30. In oneembodiment, the sensor 32 may use ultrasonic techniques to measure a“time-of-flight” that is directly related to the preload 40 on thefastener 30. A voltage pulse applied to the sensor 32 at 42 propagatesthrough the shank 44 as an ultrasonic wave 46 that is reflected off ofthe end 48 of the fastener 30 and travels back along the return path 50to the sensor 32. The ultrasonic wave 46 is returned as an echo 52 thatis recorded by the sensor 32, and which has a time-of-flight 54 that isdirectly proportional to the preload of the fastener 30. Evaluating achange in the time-of-flight 54 relative to a zero load time-of-flightallows direct measurement of the preload 40. During tightening, thefastener 30 elongates with load while the speed of the ultrasonic wave46 reduces with increasing fastener stress, resulting in an increase inthe total time-of-flight 54 that is directly proportional to the preload40. As previously mentioned, while an ultrasonic type sensor 32 has beenillustrated, other sensors and transducers using other types oftechnologies may be possible.

Attention is now directed to FIG. 5 which illustrates additional detailsof the electronic circuit 86 that is housed within the cap 66 (FIG. 4)and is coupled with both the sensor 32 and the antenna 88. In thisembodiment, the circuit 86 includes a radio frequency (RF) receiver 91and an RF transmitter 92 which may be combined into a single circuitforming a transceiver (not shown). An RF signal transmitted from thereader 38 (FIG. 1) representing a fastener query is delivered by thereceiver 91 to an electronic converter 94 which converts the received RFsignal into electrical power that may be stored in an electrical energystorage device 96, such as a capacitor or other storage medium (notshown). The RF query signal may comprise a series of pulses that aresuccessively stored until the energy stored in the storage device 96 issufficient to initiate a read cycle. The circuit 86 may also be poweredby one or more alternate power sources 98, such as a battery, energyharvesters or other power generators (not shown). For example, thealternate power source 98 may comprises an energy harvesting devicewithin the cap 66 that harvests ambient energy such as thermal energyproduced by temperature fluctuations in the fastener 30. This form ofenergy harvesting device may employ a phase change material as a heatsink against temperature fluctuations in the fastener 30, which may besignificant in the case of an aircraft during climb/decent. Energyharvesting devices using other technologies may be employed, includingbut not limited to those that harvest vibrational energy produced byatmospheric pressure changes during climb/decent of an aircraft.

As the cap 66 is being installed on the fastener 30, the contacts 82, 84are brought into engagement with the fastener 30 and the sensor 32,causing the switch 106 to close. Closure of the switch 106 readies thecircuit 86 for operation. In the event that the cap 66 is subsequentlyremoved from the fastener 30, causing the contacts 82, 84 to disengagefrom the fastener 30, the switch 106 opens and causes a unique digitalidentification (ID) number 104 in the data storage 102 to be erased.This feature may assure that a particular ID is permanently and reliablyassociated with only one particular fastener 30.

Energy stored in the energy storage device 96 is used to fire a pulsegenerator 110, as a stimulus pulse generator, which causes the sensor 32to produce an ultrasonic pulse 46 (FIG. 2) that propagates through thefastener 30, as previously described. A pulse detector circuit 112senses the return pulse and delivers the return pulse to a pulsemeasurement circuit 114 which measures the time-of-flight of the pulse.The measured time-of-flight, which represents a parameter related to thestress on the fastener 30, is delivered to a data packet circuit 116which combines the time-of-flight measurements with other data into adata packet. For example, the unique digital ID number 104 stored indata storage 102 in the circuit 86 may be combined with thetime-of-flight information into a data packet. The data packet istransmitted through an RF transmitter 92 and the antenna 88 back to thereader 38 (FIG. 1). In some embodiments, the circuit 86 may include amicroprocessor 100 to control various components of the circuit 86and/or to perform calculations. For example, the microprocessor 100 maycompare a fastener ID contained in the RF signal received from thereader 38 to the digital ID 104 in data storage 102 in order to verifythat the query is intended for the particular fastener 30 that receivesthe query signal. Once a match between these two IDs is confirmed,measurement and transmission functions may be carried out by the circuit86.

Attention is now directed to FIG. 6 which broadly shows the steps of amethod of wirelessly collecting data from one or more fasteners 30, suchas fastener preload. Beginning at 118, a unique ID is assigned to eachof a plurality of the caps 66. This unique ID may be a random ID, or maybe related to a specific bolt location in a structure, or may beotherwise assigned. At 120, a cap 66 is installed on each of thefasteners 30. At step 122, an activation signal along with a digital IDis transmitted from the reader 38 to the cap 66. At 124, the digital IDis stored in the cap 66, thereby readying the cap 66 for operation.

The data collection process begins at step 126 in which a query or readsignal is transmitted from the reader 38 to the cap 66 on one or more ofthe fasteners 30. At 128, the query signal is received at the cap 66 andis converted into stored electrical energy within the cap 66. At 129,the ID contained in the query signal and the stored ID are compared.Assuming that the ID contained in the query signal (representing thefastener 30 that is to be read) matches the stored ID in the cap 66 onthe fastener 30 receiving the query signal, the measuring andtransmission functions are initiated, resulting in the generation of astimulus pulse at 130, using the energy stored at 128. The return pulseis detected at 132 and its time-of-flight is measured at 134. At 136, adata packet is formed which includes the measured time-of-flight andother information, such as, without limitation, fastener ID, fastenertemperature, time/date stamp, etc. At step 138, the data packet istransmitted in the form of an RF signal from the cap 66 to the reader 38where it is received and processed at step 140.

FIG. 7 illustrates the steps of an alternate method for collecting datafrom the fasteners 30. Beginning at step 144, a query signal iswirelessly transmitted from the reader 38 to the cap 66. At 146, astimulus pulse is generated which is delivered through the fastener 30.At 148, a fixed processing time delay is introduced to allow for thereliable detection of the returning ultrasonic pulse. The return pulseis detected at 150, and detection information is transmitted at 152 fromthe cap 66 to the reader 38. The return pulse is received at the reader38, as shown at step 154, following which the reader 38 measures thetime between the RF start pulse and the RF finish pulse, and thensubtracts the fixed processing time delay and computes the ultrasonictime-of-flight as the difference between these two pulses as shown at156. This embodiment may reduce and simplify the electronics 86 in thecap 66 since the cap 66 no longer makes a timing measurement.

Referring now to FIG. 8, data may be collected remotely from fasteners30 installed on structures, such as an aircraft 158, using either mobilereaders 160 or fixed readers 162 that are located remote from thefasteners 30. For example, mobile readers 160 may be used by maintenancetechnicians either onboard the aircraft 158 or on the ground to monitorthe status of the fasteners 30, including fastener preload.Alternatively, readers 162 at fixed locations onboard the aircraft 58may be used to periodically monitor fastener status by collectingfastener data that may be stored for future use or sent to an onboardserver (not shown) for analysis. Similarly, a fixed, ground basedmonitoring system 166 may wirelessly collect the data from the fasteners30 which is then processed locally by a computer 168 and stored at 170as part of maintenance records, and/or wirelessly transmitted by areceiver/transmitter 172 to other sites.

The disclosed method and apparatus may also be advantageously employedin a factory production setting or in a maintenance facility settingwhere structures such as the aircraft 158 are being assembled orserviced. For example, fixed or mobile readers 174 may be installed on aceiling 176 or embedded in/under a floor or into toolingfixtures/stands/scaffolding (all not shown) of a factory in which theaircraft 158 is being assembled. The readers 174 may collect data suchas preload from the fasteners 30 as the aircraft 158 is being assembledin order to verify that fasteners 30 are properly installed and/ortorqued to specifications.

In some applications, it may be desirable to deliver signals between thereader 38 and the fasteners 30 through wireless transmissions that aresubstantially directional along a relatively narrow path, rather thanomni-directional. Directional transmissions may be more effective thanomni-directional transmissions since a larger fraction of thetransmitted signal energy reaches its intended destination, i.e. thefastener 30 or the reader 38. This technique may improve battery life aswell as the time required to query each fastener 30.

Referring now to FIG. 9, a suitable radio frequency reader 180 may bepackaged as a handheld device used by maintenance technicians to readfastener data where access to the fastener 30 may be difficult, as inthe case of the tail section 178 of an aircraft 158. In this embodiment,the reader 180 includes a pistol grip 182 that allows the user to orientand aim the reader 180 toward a desired fastener 30. The reader 180includes a directional antenna 184 comprising one or more dipolesarranged as a phased array that is used to transmit query signals andreceive responsive RF signals from the fasteners 30 containing datapackets. In this embodiment, the operator first physically locates afastener 30 to be measured and then points the reader 180 at thefastener to take the measurement. The reader 180 may further include anaiming device such as a laser 186 which directs a laser beam 188 towarda particular one of the fasteners 30. The laser beam 188 is aligned withthe orientation of the directional antenna 184 so that by pointing thelaser beam 188 toward a particular fastener 30, the transmission path ofthe antenna 184 is automatically aligned toward the fastener 30. Thisembodiment may further improve the energy efficiency of the system,extend battery life and/or reduce labor hours required to measure thestress of a given set of fasteners 30.

FIG. 10 shows the laser beam 188 having been directed toward aparticular fastener 30. With the antenna 184 aligned in the direction ofthe fastener 30, an RF signal is transmitted along a relatively narrowpath 194 (FIG. 11) from the antenna 184 to the fastener 30 (FIG. 11).Other techniques may be employed to concentrate an RF signal along arelatively narrow path. For example, an antenna dish 196 (FIG. 12) maybe employed to concentrate or focus an RF signal along a relativelynarrow path 194 toward a fastener 30 as shown in FIG. 12. Directionalantennas may be preferred in some applications over omni-directionalantennas, in order to reduce possible radio frequency interference (RFI)and/or to reduce the amount of power that is required to transmit thesignal. The antenna 88 (FIG. 4) housed in the cap 66 may similarly beconfigured in the form of a directional antenna in order to reduce thepower consumed in sending the data packet to the reader 180.

Other forms of communication techniques may be employed to collectfastener data according to the disclosed embodiments, including acoustic(sonic) energy and electromagnetic energy in the visible andnear-visible frequency ranges, sometime referred to as light energy. Forexample, as shown in FIG. 13, pulses of infrared light may be employedto transmit query signals to fasteners 30 in which an infrared diode 200produces pulses of infrared light 202 that are focused into a narrowerbeam of pulses 206 by a suitable lens 204. The lens 204 and the reader38 are aimed at a fastener 30 so that the infrared pulse beam 206impinges upon a desired fastener 30 to initiate a read cycle. FIG. 14illustrates the use of a reflective dish 208 for concentrating lightproduced by an infrared diode 200 into a concentrated pulse beam 210.Aiming of the beam 210 toward a desired fastener 30 is controlled by theorientation of the dish 208 which may be mounted on the reader 38. Theuse of infrared signals may be desirable in “noisy” RF environments suchas factories or airports. In the infrared communication system describedabove, shorter wavelengths may allow higher gain factors and may be moredesirable in some applications.

FIG. 15 illustrates the use of a laser aimer 186 in combination with aninfrared transmitter 212 to locate and query a desired fastener 30. Thelaser aimer 186 produces a visible laser beam 188 which the user mayemploy to locate and aim the infrared transmitter 212. Once thetransmitter 212 is properly aimed, an infrared query signal 195 is sentto the fastener 30, thereby initiating a read cycle.

FIG. 16 illustrates the use of a conventional, visible light source 214,such as an ordinary flashlight that is mounted on an infraredtransmitter 212. The light source 214 produces a visible light beam 216that is used to illuminate a fastener 30. A retro-reflective material218 may be placed on the fastener 30 in order to assist in reflectinglight from the light source 214 so that the fastener 30 is more visibleto a technician. Aiming of the light beam 216 at the fastener 30automatically aligns the infrared transmitter 212 so that the RF signalis directed toward the fastener 30.

In another embodiment, as shown in FIG. 17, a reader 38 may employ apistol grip 182 and an optical sight 220 to aim the reader 38 toward adesired fastener 30 in those applications where the reader 38 generatesdirectional query signals.

As previously discussed in connection with FIG. 4, it may be desirableto sense the temperature of the fastener 30 in order to adjusttime-of-flight information and improve the accuracy of preloadmeasurements. In the case of the embodiment shown in FIG. 4, atemperature sensor 90 for this purpose is incorporated into the cap 66.Other techniques, however, may be employed to sense the temperature of afastener 30, or of the structure 34 immediately surrounding the fastener30 which normally will have a temperature that is substantially the sameas that of the fastener 30. For example, as shown in FIG. 18, anon-contact temperature sensor 224 may be incorporated into the reader38 in order to remotely sense the temperature of a fastener 30. Thetemperature sensor 224 may comprise any of various known non-contacttemperature sensing devices, such as, without limitation, pyrometers,infrared thermal imaging cameras, line measuring thermometers, spotradiometers and infrared radiation thermometers. Typical infraredradiation thermometers measure infrared emissions in at least twowavelength bands, compute the ratio of intensities of the two bands anduse that ratio to estimate a temperature of the emitting surface.

FIG. 19 illustrates a handheld gun-type reader 38 which incorporates aninfrared radiation thermometer 228 and a laser beam 188 to aid in aimingthe reader 38. The reader 38 may include a display screen 230 andsuitable controls 234 which are used to actuate the laser beam 188, takea fastener temperature reading and initiate a query signal that isautomatically associated with the sensed temperature. The display screen230 along with one or more programs (not shown) stored in the reader 38may be used to show the user where each fastener 30 is located to assistin aiming the reader 38.

Attention is now directed to FIG. 20 which illustrates the steps of amethod of collecting fastener data which includes adjusting fastenerparameter measurements for variations in the temperature of the fastener30. At 236, a data packet containing time-of-flight information isreceived at the reader 38, following which the time-of-flight data isextracted at 238. The temperature of the fastener 30 is remotely sensedat 240 and is associated with the particular fastener 30 at 242. At 244,the temperature associated with the fastener is used to adjust thetime-of-flight data, as shown at 244, following which parameters ofinterest, such as fastener stress may be calculated at 246.

FIG. 21 illustrates the basic components of a reader 38 employing aremote temperature sensor 252. The reader 38 includes a receiver 248 forreceiving data packets from the fasteners 30, along with the remotetemperature sensor 252, a processor 250 and fastener ID storage 254. Theprocessor 250 associates fastener ID in storage 254 with the temperatureof a fastener 30 sensed by the remote temperature sensor 252. Theprocessor 250 may perform calculations that include adjustment of thetime-of-flight data and calculates the parameters of interest, such aspreload on the fastener 30.

FIG. 22 illustrates the use of an acoustic reader 256 that is used tocollect data from a plurality of fasteners 30 installed on the structure34 using acoustic signal communications. In this embodiment, theacoustic reader 256 is brought into physical engagement with thestructure 34, and an acoustic signal 260 is transmitted from the reader256 through the structure 34 to each of the fasteners 30. Thus, thestructure 34 acts as the transmission medium for carrying acousticenergy signals between the reader 256 and the fasteners 30. The use ofan acoustic reader 256 is particularly advantageous where the fasteners30 are located inside a closed structure made of materials such ascomposites that may not be transparent to electromagnetic radiationsignals. Long wavelength acoustic signals may generally propagatethrough most structures farther than short wavelength signals, however,but the data rate of long wavelength signals may be less than for shortwavelength signals. Thus, it may be desirable to provide the user withthe option of selecting two or more communication wavelengths.

FIG. 23 illustrates another embodiment of the apparatus in which adirectional acoustic reader 256 is employed to direct an acoustic querysignal 260 a along relatively narrow path through a structure 34 to aparticular fastener 30. This embodiment may be advantageous in someapplications where it is necessary to focus energy along the relativelynarrow path in order to reach a particular fastener 30.

FIG. 24 shows the overall components of apparatus for collectingfastener data using acoustic signals. The acoustic reader 256 broadlycomprises an acoustic transducer 262 that produces acoustic signals of adesired wavelength controlled by a wavelength selector 263. Thewavelength of the acoustic signal may be selected to best suit thecharacteristics of the particular structure 34 on which the fasteners 30are installed. The reader 256 further includes an acoustic coupler 264which is placed into contact with the structure 34 and functions tocouple the acoustic signal from the transducer 262 into the structure34. In some embodiments the reader 256 may include an acoustic powermeter 265 which allows a user to optimally adjust the direction ofdirectional beam 260 a which will optimally adjust the directionalorientation of coupler 264.

The acoustic signal, indicated by the broken line 260, is received atthe cap 66 on a particular fastener 30. The cap 66 includes an acousticcoupler 266 which couples the received acoustic signal to a transducer267 in the cap 66. The transducer 267 converts the acoustic signal intoelectrical power that may be stored in the energy storage 272 and usedto drive a pulse generator 270 which sends pulses to a sensor (notshown) on the fastener 30 for measuring preload. Similar to the caps 66described earlier, the cap 66 may include storage 268 for storing thefastener ID, as well as a temperature sensor 274. Although notspecifically shown in FIG. 24, the cap 66 may further include aprocessor and/or transmitter that is used to transmit data packetsthrough the structure 34 to the reader 256.

Attention is now directed to FIG. 25 which illustrates the steps of amethod of collecting fastener data using acoustic signals. Beginning at276, the desired communication wavelength is selected which is bestsuited for the particular structure 34 on which the fasteners 30 areinstalled. At 278, a particular fastener 30 is selected to be queried.At 280, the acoustic reader 256 is brought into physical contact withthe structure 34 containing the fastener 30 to be queried. Next, at 282,one or more acoustic signals in the form of one or more acoustic pulsesare generated, and at 284, the ID of the fastener to be queried is codedinto the pulse(s). At 286, the coded pulses are transmitted into thestructure 34 using an acoustic coupler 264 (FIG. 24). At 288, theacoustic pulses are received at the queried fastener 30, following whicha check is made at the fastener 30 to verify that the received ID codematches the ID of the queried fastener, as shown at step 290.

At 292, the acoustic energy pulse is stored and is used to generate andtransmit an internal pulse into the fastener 30. At 294, thetime-of-flight of the internally transmitted pulse is measured.Optionally, at 296, the temperature of the queried fastener is measured.At step 298, the time-of-flight data along with temperature and otherdata is loaded into a data packet which is transmitted at 300 in theform of acoustic pulses which propagate through the structure 34 to thereader 256. At step 302, the acoustic pulses from the fastener 30 arereceived at the reader 256 and are processed to determine the stress onthe fastener 30.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine and automotive applications. Thus, referringnow to FIGS. 26 and 27, embodiments of the disclosure may be used in thecontext of an aircraft manufacturing and service method 320 as shown inFIG. 26 and an aircraft 322 as shown in FIG. 27. During pre-production,exemplary method 320 may include specification and design 324 of theaircraft 322 and material procurement 326 in which the disclosedembodiments may be specified for use in installing and/or monitoringfasteners in the aircraft 322. During production, component andsubassembly manufacturing 328 and system integration 330 of the aircraft322 takes place. The disclosed embodiments may be used to install andmonitor fasteners used in the components and subassemblies. Thereafter,the aircraft 322 may go through certification and delivery 332 in orderto be placed in service 334. While in service by a customer, theaircraft 322 is scheduled for routine maintenance and service 336 (whichmay also include modification, reconfiguration, refurbishment, and soon). The disclosed method may be used to check or monitor the preload offasteners during certification 332 and/or during the maintenance andservice 336.

Each of the processes of method 320 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 27, the aircraft 322 produced by exemplary method 320may include an airframe 338 with a plurality of systems 340 and aninterior 342. Examples of high-level systems 340 include one or more ofa propulsion system 344, an electrical system 346, a hydraulic system348, and an environmental system 350. Any number of other systems may beincluded. The disclosed embodiments may be used to install and/ormonitor fasteners in joints forming part of the airframe 338, or oncomponents forming part of the propulsion system 344 or the hydraulicsystem 348. Although an aerospace example is shown, the principles ofthe disclosure may be applied to other industries, such as the marine,heavy equipment, power generation, refinery, and automotive industries.

The disclosed embodiments may be employed to measure the preload offasteners installed on the aircraft 322 during any one or more of thestages of the production and service method 320. For example, componentsor subassemblies corresponding to production process 328 may incorporatefasteners requiring accurate measurement of preload. Also, one or moremethod embodiments, or a combination thereof may be utilized during theproduction stages 328 and 330, for example, by substantially expeditingassembly of or reducing the cost of an aircraft 322.

Although the embodiments of this disclosure have been described withrespect to certain exemplary embodiments, it is to be understood thatthe specific embodiments are for purposes of illustration and notlimitation, as other variations will occur to those of skill in the art.

What is claimed is:
 1. A system, comprising: a cap; a fastener thatincludes a sensor, wherein the cap is configured to couple to thefastener; a signal receiver within the cap, the signal receiverconfigured to receive a signal from a reader; an electronic converterconfigured to convert the signal from the reader into electrical energy;an energy storage device configured to store electrical energy from theelectronic converter; a pulse generator configured to use electricalenergy stored by the energy storage device to trigger the sensor toproduce an ultrasonic pulse when the cap is coupled to the fastener; apulse detector circuit configured to sense a reflected pulse due to theultrasonic pulse; a pulse measurement circuit configured to generatemeasurement data based on the reflected pulse; and a signal transmitterconfigured to transmit the measurement data to the reader.
 2. The systemof claim 1, further comprising: an energy harvesting device coupled tothe energy storage device, wherein the energy harvesting device harveststhermal energy produced by temperature fluctuations, wherein theharvested thermal energy may be stored in the energy storage device. 3.The system of claim 1, wherein the signal receiver is selected from thegroup consisting of a light signal receiver, a radio frequency signalreceiver, and an acoustic signal receiver.
 4. The system of claim 1,wherein the cap further includes a temperature sensor for sensing atemperature of the fastener and wherein the signal transmitter isfurther configured to transmit an indication of the temperature to thereader.
 5. The system of claim 1, further comprising: a directionalantenna within the signal receiver tuned to receive the signal via anarrow path from the reader.
 6. The system of claim 5, wherein thedirectional antenna is one of a directional dipole antenna and a dishantenna.
 7. The system of claim 1, further comprising: electricalcontacts configured to connect circuitry located within the cap to thesensor when the cap is coupled to the fastener.
 8. The system of claim1, further comprising: a data packet circuit configured to receive themeasurement data and convert the measurement data into a data packet fortransmission via the signal transmitter.
 9. The system of claim 1,further comprising: a data storage device configured to store anidentifier received from the reader.
 10. A method comprising: receivinga signal at a cap from a reader, the cap being coupled to a fastener;converting the signal into electrical energy and storing the electricalenergy at an energy storage device; triggering a sensor to produce anultrasonic pulse using the stored electrical energy; sensing a reflectedpulse from the ultrasonic pulse; and generating measurement data basedon the reflected pulse and transmitting the measurement data to thereader.
 11. The method of claim 10, further comprising: harvestingthermal energy produced by temperature fluctuations as additionalelectrical energy; and storing the additional electrical energy at theenergy storage device.
 12. The method of claim 10, wherein receiving thesignal comprises receiving a light signal, a radio frequency signal, oran acoustic signal receiver.
 13. The method of claim 10, furthercomprising: sensing a temperature of the fastener; and transmitting anindication of the temperature to the reader.
 14. The method of claim 10,wherein receiving the signal comprises tuning a directional antenna toreceive the signal via a narrow path from the reader.
 15. The method ofclaim 10, further comprising: connecting circuitry located within thecap to the sensor within the fastener when the cap is coupled to thefastener.
 16. The method of claim 10, further comprising: converting themeasurement data into a data packet for transmission to the reader. 17.The method of claim 10, further comprising: receiving an identifier fromthe reader along with the signal; and matching the identifier to astored identifier before triggering a sensor to produce an ultrasonicpulse.
 18. A method comprising: joining at least two separate structuralmembers together using a fastener; installing a cap to the fastener;transmitting an activation signal from a reader to a signal receiverwithin the cap, the activation signal including an identifier to bestored within the cap; transmitting a query signal from the reader tothe signal receiver within the cap, wherein the query signal includesthe identifier, and wherein energy from the query signal powers a pulsegenerator in the cap to trigger a sensor to produce an ultrasonic pulsefor measuring a time-of-flight; and receiving measurement data from thecap, the measurement data including the time-of-flight.
 19. The methodof claim 18, wherein the cap matches the identifier to a storedidentifier before transmitting the measurement data.
 20. The method ofclaim 18, wherein the pulse generator is further powered by thermalenergy fluctuations.